Sabine Lake Research Articles

Intercomparison of Surface Currents Obtained Using SCHISM and the HF Radar Data in Galveston Bay and Sabine Lake, Texas

Intercomparison of Surface Currents Obtained Using SCHISM and the HF Radar Data in Galveston Bay and Sabine Lake, Texas

Assessing compound flooding potential with multivariate statistical models in a complex estuarine system under data constraints

AbstractCompound flooding may result from the interaction of two or more contributing processes, which may not be extreme themselves, but in combination lead to extreme impacts. Here, we use statistical methods to assess compounding effects from storm surge and multiple riverine discharges in Sabine Lake, TX. We employ several trivariate statistical models, including vine‐copulas and a conditional extreme value model, to examine the sensitivity of results to the choice of data pre‐processing steps, statistical model setup, and outliers. We define a response function that represents water levels resulting from the interaction between discharge and surge processes inside Sabine Lake and explore how it is affected by including or ignoring dependencies between the contributing flooding drivers. Our results show that accounting for dependencies leads to water levels that are up to 30 cm higher for a 2% annual exceedance probability (AEP) event and up to 35 cm higher for a 1% AEP event, compared to assuming independence. We also find notable variations in the results across different sampling schemes, multivariate model configurations, and sensitivity to outlier removal. Under data constraints, this highlights the need for testing various statistical modelling approaches, while the choice of an optimal approach remains subjective.

Estuary‐Level Genomic Variation Confirms Demographic and Life History Differences among Black Drum Populations in Texas

AbstractThe Black Drum Pogonias cromis is a year‐round resident in estuarine and nearshore habitats throughout the Gulf of Mexico and is common in Texas. Multiple studies have highlighted life history and demographic variation in this species among estuaries, and tagging studies conducted in Texas suggest limited migration between adjacent estuaries. While these findings raise the potential for genetic heterogeneity among estuaries via accumulation of genetic drift, such an effect has never been tested. We used 5,340 genomic single nucleotide polymorphisms from a reduced‐representation genomic library to assess the magnitude and geographic pattern of genetic heterogeneity in Black Drum sampled from multiple estuaries in Texas. We found significant genetic heterogeneity that could be partitioned into three regional groupings: northern (Sabine Lake to San Antonio Bay), central (upper Laguna Madre and its secondary bays) and southern (lower Laguna Madre). These regional groupings roughly coincide with significant differences in life history strategies noted in previous studies and suggest a regional stock structure that is anchored by two independently collected lines of evidence. There was also evidence for weak but significant genetic structure among adjacent secondary estuaries within the Baffin Bay complex. Finally, outliers from the genomic data set correlated weakly (but significantly) with differences in residual growth among individuals. These findings imply genetic heterogeneity of Black Drum among and within estuaries, correlation of growth phenotypes with a small partition of outlier loci, and correlation between genomic patterns and complex regional differences in life history phenotypes described previously. Stock assessments for this species should carefully consider regional stock definitions and model parameters because such inputs may vary significantly above and below the scale of estuaries.

The integration of fatty acid biomarkers of trophic ecology with pollutant body-burdens of PAHs and PCBs in four species of fish from Sabine Lake, Texas

This study investigated whether the composition of fatty acids in hepatic tissue of four fish species from Sabine Lake (TX), influenced hepatic body-burdens of pollutants. The multivariate correlations between hepatic body-burdens of sixteen polycyclic aromatic hydrocarbons (PAHs) and twenty-nine polychlorinated biphenyls (PCBs), with thirty-seven fatty acids was studied. The trophic ecology of fish was determined using stomach content analysis and by comparing characteristic fatty acid profiles. The fish species studied included: bull shark (Carcharhinus leucas), alligator gar (Atractosteus spatula), red drum (Sciaenops ocellatus), and gafftopsail catfish (Bagre marinus). Assessment of fish stomach contents demarcated catfish and red drum (mainly invertebrate diet) vs. alligator gars and bull sharks (mainly teleost diet). Elevated levels (45× higher) of nervonic acid (24:1n9) also placed the trophic ecology of catfish and red drum closer to the base of the marine/estuarine food web of Sabine Lake, as compared to alligator gars and bull sharks. PAH profiles showed a predominance of low molecular weight PAHs (≤3 aromatic rings) in catfish, red drum and alligator gars. Bull sharks exhibited the highest levels for select high molecular weight PAHs (≥ 4 aromatic rings). The overall predominance of low molecular weight PAHs indicated exposure to mainly petrogenic sources of PAHs. Bull sharks and alligator gars also exhibited the highest body-burdens of PCBs. The risk assessment of dioxin-like PCBs showed median toxic equivalent (TEQ) values in bull sharks to be the highest, and above the upper toxicity thresholds for adverse effects in fish and aquatic mammals. The multivariate correlational analysis of pollutant body-burdens and fatty acid levels showed no clear correlation of the pollutants with any particular type of fatty acid (unsaturated vs. saturated, short-chain vs. very-long chain). This result indicates that pollutant bioaccumulation was not associative with the specific fatty acid composition of lipids in the fish from Sabine Lake.

Overview of statewide geophysical surveys for ecosystem restoration in Louisiana

The System Wide Assessment and Monitoring Program (SWAMP) was implemented by the Louisiana Coastal Protection and Restoration Authority (CPRA) to develop an Adaptive Management Implementation Plan (AMIP). SWAMP ensures that a comprehensive network of coastal data collection/monitoring activities is in place to support the development and implementation of Louisiana’s coastal protection and restoration program. Monitoring of physical terrain is an important parameter of SWAMP. For the first time a systematic approach was adopted to undertake a geophysical (bathymetric, side-scan sonar, sub-bottom profile, and magnetometer) survey along more than 5,000 nautical miles (nm) (excluding the 1,559 nm currently being surveyed from west of Terrebonne Bay to Sabine Lake) of track-line in almost all of the bays and lakes from Chandeleur Sound in the east to Terrebonne Bay in the west. This data collection effort complements the regional bathymetric survey undertaken under the Barrier Island Comprehensive Monitoring (BICM) Program in the adjacent offshore areas. This paper describes how a study of this magnitude was conceptualized, planned, and executed along the entire Louisiana coast. It is important to note that the initial intent was to collect bathymetric data only for numerical modelling for ecosystem restoration and storm surge prediction. Geophysical data were added for oyster identification and delineation. These first-order data also help comprehend the regional subsurface geology essential for sediment exploration to support Louisiana’s marsh and barrier island restoration projects.

Intraspecific Aggression Towards Common Bottlenose Dolphin Calves, Northern Gulf of Mexico

Infanticide has been widely documented throughout the animal kingdom, and has generally been viewed as an evolved, or adaptive behavior for the perpetrators. Infanticide motivated by increased sexual access to females with calves, or the elimination of potential genetic competition in the form of calf-directed aggression or infanticide, has been proposed for delphinids including killer whales, Indo-Pacific humpback dolphins, Guiana dolphins, and bottlenose dolphins. However, reports of intraspecific aggression towards bottlenose dolphin calves are relatively infrequent, and accounts of confirmed infanticide are rarer still. Reporting instances of intraspecific calf-directed aggression aids researchers to better understand the socio-behavioral context of these aggressive interactions. Here, we report an incident of conspecific aggression towards a calf in a small group of common bottlenose dolphins near Sabine Lake, northwestern Gulf of Mexico. We discuss the behavioral context, and surveyed other researchers to attempt to gauge the prevalence of perceived aggressive interactions among the bottlenose dolphin groups they study in the northern Gulf of Mexico.

Calibration and Validation of Hydrodynamics and Salinity Transport Model for Sabine Lake Water System

In this study, a hydrodynamic and a salinity transport models were developed for simulations of Sabine Lake water system located on the Texas-Louisiana border. The target simulation area includes several major water bodies, such as Sabine Lake, Sabine River, Sabine Pass, Sabine Neches Canal (Ship Channel), and part of Gulf Intracoastal Waterway (GIWW) and Sabine River Diversion Canal (SRDC). The SRDC supplies fresh water to the area industry, mainly petrochemical. High salinity in SRDC could significantly affect the daily production of the industry. Two-dimensional (2D) depth-averaged shallow water equation set and 2D depth-averaged salinity transport equation were used for developing the hydrodynamic and salinity transport numerical models in order to carry out the simulation. The major purposes of this study are to calibrate and validate hydrodynamic and salinity transport models in order to assess and predict the salinity in SRDC under severe weather conditions such as hurricane storm surges in future study. Measurement data from National Oceanic and Atmospheric Administration (NOAA) and United States Geological Survey (USGS) were used to calibrate the boundary conditions as well as to validate the model. Boundary conditions were calibrated at locations in Sabine Pass and in the north edge of the lake by using water–surface elevation data. Hydrodynamic model was validated at the USGS location using water–surface elevation data. Then, the simulation estimations of water surface level and salinity were compared at three locations, and the results show the accuracy of the validated model. Parallel computing was conducted in this study as well, and computational efficiency was compared.

An Engraved Bulbous-Necked Caddo Bottle from 41OR33 at the mouth of the Sabine River, Orange County, Texas

41OR33 is a large prehistoric shell midden deposit in Orange County, Texas, about 8.5 miles southwest of the city of Orange, at the mouth of the Sabine River and just north of Sabine Lake in Southeast Texas. Before the site was destroyed for road fill in October 1956, limited archaeological investigations had been done there by avocational archaeologists and then by E. Mott Davis of The University of Texas at Austin. During that work, a number of Native American burials were exposed and excavated, including one burial with an engraved bulbous-necked ancestral Caddo ceramic bottle. The bottle was donated by Edgar W. Brown, Jr. to UT in October 1956. I recently documented this vessel, which is a far-flung companion to bulbous-necked and spool-necked Caddo bottles from post-A.D. 1600 sites in the Red River and Ouachita River basins in East Texas and Southwest Arkansas as well as several post-A.D. 1600 sites in East Texas such as the Taylor site (41HS3) in the Big Cypress Creek basin.

ASSESSMENT OF THE EVOLUTION OF STORM SURGE IN COASTAL LOUISIANA

The Louisiana coastal landscape comprises an intricate system of fragmented wetlands, natural ridges, man-made navigation canals, flood protection and oil and gas infrastructure. Louisiana lost approximately 1,883 square miles (4,877 sq km) of coastal wetlands from 1932 to 2010 including 300 square miles (777 sq km) lost between 2004 and 2008 due to Hurricanes Katrina, Rita, Gustav and Ike (Couvillion et al., 2011). A projected additional 2,250 square miles (5,827 sq km) of coastal wetlands will be lost over the next 50 years if no preventative actions are taken (Coastal Protection and Restoration Authority of Louisiana, 2017). Storm surge models representing historical eras of the Louisiana coastal landscape can be developed to investigate the response of hurricane storm surge (e.g. peak water levels, inundation volume and time) to land loss and vegetative changes. Land:Water (L:W) isopleths (Gagliano et al., 1970; Twilley et al., 2016; Siverd et al., 2018) have been calculated along the Louisiana coast from Sabine Lake to the Pearl River. These isopleths were utilized to develop a simplified coastal landscape (bathymetry, topography, bottom roughness) representing circa2010. Similar methods are employed with the objective of developing storm surge models that represent the coastal landscape for past eras (circa1890, c.1930, c.1970).

Archaeological Investigations at the Mike Myers Site (41CE481) on Bowles Creek in Cherokee County, Texas

The Mike Myers site is a multiple component prehistoric site in the Bowles Creek valley in the Neches River basin in East Texas. The site is on an upland landform (400 ft. amsl), now a pasture with low surface visibility, between Bowles Creek to the east ca. 100 m and a spring-fed branch to the west. The confluence of Bowles Creek with Jackson Branch lies ca. 600 m to the south. Soils on the site are classified as Nacogdoches fine sandy loam. Based on the archaeological investigations conducted at the site to date, the known site area covers a ca. 150 x 60 m area (north-south and east-west) or approximately 2 acres, but the site may well extend to the south onto a lower upland ridge slope (390 ft. amsl) some distance; hopefully shovel tests can be excavated in this area in the near future to determine the full site boundaries. This article discusses the archaeological findings obtained to date from 2016 archaeological investigations at the Mike Myers site, much of it consisting of shovel tests across the site area, focusing particularly on the archaeological remains recovered in the work that date from Woodland and Caddo periods. Most notably, the shovel test work at the site recovered two sherds of non-tempered early Woodland period Tchefuncte pottery. As far as we are aware, this is only the second site in East Texas where Tchefuncte pottery has been found; the other site is the well-known Resch site (41HS16) in the Sabine River basin in Harrison County, Texas. Tchefuncte culture pottery has been recovered from the Louisiana Gulf Coast, in the Ouachita and Mississippi river basins in Mississippi, Louisiana, and southeast Arkansas, and in the Sabine Lake area of coastal Texas and Louisiana, more than 250 km east and southeast of the Mike Myers site.

Current–wave interaction in the Mississippi–Atchafalaya river plume on the Texas–Louisiana shelf

Wave–current interaction over the Texas–Louisiana shelf, and its effects on the dispersal and mixing of the Mississippi–Atchafalaya river plume, have been investigated using the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) Modeling System. The modeling system is driven by realistic wave and current conditions at the open boundaries and high frequency1-D wind measured from a nearby meteorological station. Skill analysis demonstrates that the model reproduces the wave and salinity fields reasonably well. Waves over the Texas–Louisiana shelf are dominated by locally forced wind seas, and generally propagate in the same direction as the winds. Investigation into the spatial differences in the effect of waves reveals two distinct dynamical regions: the Chenier shelf, the shelf region extending roughly offshore from Sabine Lake to Vermilion Bay, and the Louisiana Bight, the region between the Mississippi Delta and Terrebonne Bay. A variety of model runs are performed, where specific wave processes are either included or excluded, in order to isolate the processes acting in different regions. The Chenier shelf is mainly affected by wave enhanced bottom stress, whereas the Louisiana Bight is mostly affected by the surface wave induced mixing and 3-D wave forces. The wave enhanced bottom stress suppresses cross-shore exchange, and acts to trap more freshwater in the nearshore regions shallower than 50m over the Chenier shelf. Wave enhanced bottom stress plays only a minor role in the Louisiana Bight, where the surface-trapped Mississippi plume rarely feels the bottom. The surface intensified wave mixing and 3-D wave forces reduce the surface salinity and weaken the stratification in the region associated with the thin recirculating Mississippi plume in the Louisiana Bight. Model results indicate that the surface wave mixing, the 3-D wave forces, and the wave bottom stress exhibit little interaction over the Texas–Louisiana shelf. Finally, we have demonstrated that the one-way coupling is capable of resolving the majority of wave effects over the entire shelf if the seasonal scale is of interest.

Characterizing Nekton use of the Largest Unfished Oyster Reef in the United States Compared with Adjacent Estuarine Habitats

Characterizing density patterns of fish and crustaceans across estuarine habitat types can provide useful information regarding their relative value. The oyster reef complex within Sabine Lake Estuary is the largest known in the United States with no record of commercial harvest, and it presents a unique opportunity to understand the habitat value of an unfished reef system in comparison with adjacent estuarine habitats. High abundances of relatively large oysters with complex formations were observed throughout the 2-y study period. Average densities of fish and crustaceans were 6 times greater at the marsh edge than the nonvegetated shallow habitats, and 40 times greater than both the oyster reef and nonvegetated deep habitats. Low faunal densities observed in the oyster reef habitat may be the result of spatial configuration and connectivity to surrounding habitats, collection limitation resulting from its large vertical relief (>1 m) and complex 3-dimensional structure, or habitat selection resulting from water depth. Because the majority of crustaceans and resident and transient fish were observed within the marsh edge and nonvegetated shallow habitats, it is difficult to determine whether oyster reefs within Sabine Lake Estuary provide essential habitats for these species. Although low densities of organisms were observed in the oyster reef habitat, multivariate analysis indicates that the unfished reef supports a unique community of fish and crustaceans. Results provide a valuable baseline for future conservation, restoration, and management actions as we seek to understand more completely and to protect important estuarine habitat types.

Spatiotemporal Predictive Models for Juvenile Southern Flounder in Texas Estuaries

AbstractSouthern Flounder Paralichthys lethostigma supports a multimillion dollar commercial and recreational fishery in the Gulf of Mexico. Despite its economic importance, the Southern Flounder population has been declining for decades. To improve the management of this fishery, both population trends and changes in environmental conditions need to be considered. Using two different statistical modeling techniques, boosted regression tree (BRT) and artificial neural network (ANN), a 29‐year fisheries‐independent record of juvenile Southern Flounder abundance in Texas was examined to illustrate how environmental factors influence the temporal and spatial distribution of juvenile Southern Flounder. Boosted regression trees show the presence of juvenile Southern Flounder is closely associated with relatively low temperatures, low salinity levels, and high dissolved oxygen concentrations. Both ANN and BRT models resulted in high predictive performance with slight spatial differences in predicted distribution. Both models suggested high probability of occurrence in Galveston Bay and East Matagorda Bay. The ANN accurately predicted higher probability of occurrence in Sabine Lake compared with the BRT model. Our results will provide tools for fisheries managers to enhance management and sustainability of the Southern Flounder population. Moreover, these results also identify a predictive framework for proactive approaches to ecosystem management by providing more data to identify essential habitat features and understanding relationships between abiotic and biotic factors within those habitats.Received October 16, 2012; accepted May 22, 2013

Texas water wars: how politics and scientific uncertainty influence environmental flow decision-making in the Lone Star state

In 2007, Texas passed Senate Bill (SB) 3 mandating formation of science and stakeholder committees to make recommendations on the environmental flows (e-flows) needed to maintain the ecological integrity of river basins through a collaborative process designed to achieve consensus. The Texas Commission on Environmental Quality (TCEQ), the state agency that issues water rights permits, was to promulgate these rec- ommendations and develop e-flow rules. For the first two basins to complete the SB3 process, the Sabine and Neches Basins and Sabine Lake Bay and the Trinity and San Jacinto Basins and Galveston Bay, final e-flow rules did not mimic a natural flow regime, rather, only subsistence flows, one level of base flows, and low flow pulses at a limited number of sites were adopted. In this article, I describe why the SB3 process was derailed for these basins. Science and stakeholder committees were skewed with more members representing short-term economic than ecological and recreational interests in freshwater. Many individuals on the science and stakeholder committees worked for river authorities, semiautonomous state agencies that receive the majority of their funding from surface water sales, and consulting firms that regularly contract with the river authorities. Water rights holders were from the outset distrustful of the SB3 process. There was a high degree of uncertainty associated with e-flow science, and adaptive management was used as justification for making low e-flow recommendations. In the end, TCEQ set environmental flow rules at levels lower than those recommended for protection of environmental benefits by the science teams.

Population connectivity of red drum in the northern Gulf of Mexico

Stable carbon (δ 13 C) and oxygen (δ 18 O) isotope ratios in otoliths were used to assess the degree of connectivity between early life and adult habitats of red drum Sciaenops ocellatus in the northern Gulf of Mexico. Young-of-the-year (YOY) red drum were sampled over a 3 yr period from major estuaries along the Texas coast, and otolith δ 13 C and δ 18 O were quantified to determine whether chemical tags in otoliths were region specific. North to south gradients were pronounced for otolith δ 13 C and δ 18 O, with values being higher (enriched in the heavier isotope) for YOY red drum from southern estuaries relative to those in the north. Four distinct regional groups of YOY red drum were identified using otolith δ 13 C and δ 18 O: North (N), Sabine Lake and East Galveston Bay; North- Central (NC), Christmas Bay and Matagorda Bay; South-Central (SC), Aransas Bay and Redfish Bay; and South (S), Laguna Madre. Overall classification success to these regional nurseries was high for each year examined: 2001 (92%), 2002 (82%) and 2003 (90%). Mixed-stock analysis performed with age-2+ red drum collected in 2003 matched to the 2001 YOY baseline indicated that most of the sub- adult and adult red drum sampled in the S and SC regions were produced from the same areas (82 to 91%), with limited exchange between these regions. Mixing was more pronounced in the northern regions (N, NC), with a large percentage (35 to 42%) of individuals originating from the adjacent region to the south. Overall, the majority of sub-adult and adult red drum was collected within or near the same region occupied during the YOY period, suggestive of natal homing, retention within specific estuarine corridors, or lower survivability of recruits migrating from distant regions.

Nitrogen fixation and dissimilatory nitrate reduction to ammonium (DNRA) support nitrogen dynamics in Texas estuaries

We conducted continuous‐flow experiments on intact sediment cores from Laguna Madre, Sabine Lake, East Matagorda Bay, and Nueces Estuary to evaluate internal nitrogen (N) sources, sinks, and retention mechanisms in Texas estuaries having different salinities. Mean ammonium (NH4+) flux ranged from slight uptake (negative values) to NH4+ production rates of about 300 µmol m−2 h−1 (units used for all N rates) and increased with salinity (p = 0.10). Net nitrate (NO3−) flux (–20 to 32) and net N2 flux (–70 to 100) did not relate to salinity. Mean net N2 flux was positive but near zero, indicating that N2 sources and sinks are nearly balanced. Total denitrification, N fixation, and potential dissimilatory NO3− reduction to NH4+ (DNRA) rates were estimated after inflow water was enriched with 15NO3− (100 µmol L−1). Total denitrification rates ranged from 0 to 90 versus N fixation rates ranging from 0 to 97. Potential DNRA, measured conservatively as 15H accumulation, ranged from 0 to 80 and related significantly to salinity (p < 0.01). Increases in total NH4+ release after 15NO3− additions were higher but closely related (r = 0.9998) to 15NH4+ accumulation, implying exchange reactions of DNRA‐regenerated 15N4+ with sediment‐bound 14NH4+. The fate of NO2 was related to salinity, perhaps via sulfide effects on DNRA. Potential DNRA was high in southeastern Corpus Christi Bay in August during hypoxia when the sulfide transition zone was near the sediment surface. Nitrogen fixation and DNRA are important mechanisms that add and retain available N in Texas estuaries.

Holocene Evolution of the East Texas Coast and Inner Continental Shelf: Along-Strike Variability in Coastal Retreat Rates

ABSTRACT The low gradient east Texas coast and inner-continental shelf, from Sabine Lake at the Texas-Louisiana border to the western end of Galveston Island, experienced extreme along-strike variations in rates of Holocene coastal retreat. Around 7.7 ka a barrier shoreline was located approximately 55 km offshore. Toward the western end of Galveston Island, the shoreline retreated 55 km, occupying a position on the lagoon side of the Island by about 5.3 ka. Toward the Texas-Louisiana border, the shoreline retreated more gradually, occupying a position seaward of Sabine Bank by 5.3 ka. Between 4.7 ka and 2.8 ka the shoreline at Sabine Bank retreated 30 km, while Galveston Island prograded seaward. Bolivar Peninsula began to accrete around 1.5 ka. Heald and Sabine banks, located on the inner continental shelf above terraced fluvial deposits of the Trinity-Sabine incised valley, are the only preserved remnants of these former shoreline positions. Fluctuating rates of sea-level rise were not the forcing mechanism behind episodes of rapid shoreline retreat because these events were localized. Rather, along-strike variations in the rate of transgression were caused by the variable inner-shelf gradients, which increase towards the west, and the orientation of the Sabine incised valley and associated terraced fluvial deposits, which trend northeast-southwest (parallel to shore). As shorelines retreated over fluvial deposits, these served as local sand sources that enabled barrier islands to persist Figure 1. Map of the east Texas inner shelf showing locations of Sabine, Heald, and Shepard banks. Paleotopographic map of the Pleistocene surface (thin contours; Siringan 1993) delineates the Trinity-Sabine incised valley, which formed during the last lowstand of sea level (Thomas and Anderson 1994). Bathymetric contours are shown as thick lines with bold numbers. Dots are core locations. End_Page 405------------------------ offshore, out of equilibrium with sea level. Once these sand sources became depleted, and/or sea level reached some critical threshold, barrier shorelines became stranded offshore as banks, and new shorelines formed landward. The geologic setting of coastal areas, specifically antecedent topography, plays a primary role in controlling coastal evolution. To accurately forecast long-term (centennial to millennial) coastal evolution, it is essential that impacts associated with variations in the underlying geology of coastal areas be incorporated into coastal forecasting models.

Use of In Situ Burning as an Oil Spill Response Tool: Follow-Up of Four Case Studies

ABSTRACT Four in situ burning sites that varied widely in the physical setting, oil type, timing of the burn, and post-burn treatment were assessed 0.5–1.5 years post-burn: two condensate spills in intertidal marshes at Mosquito Bay, LA in April 2001 and near Sabine Lake, LA in February 2000; crude oil spill in a ponded wetland in Minnesota in July 2000; and a spill of diesel in a salt flat/wetland north of Great Salt Lake, UT in January 2000. When used quickly after a release, burning is most effective at reducing damage to vegetation and the areal extent of impact. Where crude oil was burned within hours after the release at the Minnesota site, the impact area was restricted to 3 acres. In contrast, the diesel in the Utah spill spread over 38 acres within 3 days. The window of opportunity for in situ burning to be an effective means of oil removal can be days to months, depending on the spill conditions. The condensate spill at Mosquito Bay site was effectively burned 6–7 days after the release was reported. For spills with snow and ice cover, burning may still be effective months later. In fact, it may be necessary to consider additional burns during thaw periods and during the final thaw. Burning will not reduce the toxic effects of the oil that occurred prior to the burn. It can, however, be very effective at reducing the extent and degree of impacts by quickly removing the remaining oil. In three of the four case studies, the area burned was significantly larger than the oiled area (up to 10 x). Healthy, green, unoiled vegetation is not always an effective fire break, particularly downwind; fires can quickly jump the kinds of fire breaks placed during spill emergencies in wetlands (e.g., vegetation laid down by the passage of airboats).

Salinity modelling for the Sabine?Neches Estuary, Southeast Texas

A two-dimensional, depth averaged, computer code was used to model salinities for the Sabine–Neches Estuary in Southeast Texas, USA. The model bathymetry was set to the mean sea level of 1996, and channel friction was adjusted to give an optimised Manning's n value for the annual, 6-minute water level data at eight stations.The simulated velocities were checked using flow discharges measured at six estuary sections for a three-day survey period. Three dispersion methods were used to calibrate the model for salinity. The data used were a 6 month record for 1996 at seven estuary stations, and a 7-year partial record from 1990 to 1996 for two stations at the Upper and Lower ends of Sabine Lake. The first method used a constant salinity dispersion coefficient and the second used a velocity related coefficient; they were accurate to within an annual mean value of about 5 ppt. For the third method, a two dimensional dispersion function was derived, which modelled to within an annual mean value of about 1 ppt. The ultimate purpose for the study was to estimate salinity increase for Sabine Lake with designed, fresh water flow extractions from the catchment. A maximum salinity increase of about 2 ppt for a 50 year return period was estimated.

Salinity modelling for the Sabine—Neches Estuary, Southeast Texas

A two-dimensional, depth averaged, computer code was used to model salinities for the Sabine–Neches Estuary in Southeast Texas, USA. The model bathymetry was set to the mean sea level of 1996, and channel friction was adjusted to give an optimised Manning's n value for the annual, 6-minute water level data at eight stations.The simulated velocities were checked using flow discharges measured at six estuary sections for a three-day survey period. Three dispersion methods were used to calibrate the model for salinity. The data used were a 6 month record for 1996 at seven estuary stations, and a 7-year partial record from 1990 to 1996 for two stations at the Upper and Lower ends of Sabine Lake. The first method used a constant salinity dispersion coefficient and the second used a velocity related coefficient; they were accurate to within an annual mean value of about 5 ppt. For the third method, a two dimensional dispersion function was derived, which modelled to within an annual mean value of about 1 ppt. The ultimate purpose for the study was to estimate salinity increase for Sabine Lake with designed, fresh water flow extractions from the catchment. A maximum salinity increase of about 2 ppt for a 50 year return period was estimated.